Die casting system for amorphous alloys

ABSTRACT

Provided is a system and method for metering an amount of molten amorphous alloy into a mold cavity of an injection system. A melting chamber in the system is heated to or above a solidus temperature of the alloy to form a hot chamber. Both the chamber and mold are maintained in an inert atmosphere. The molten alloy is metered from the chamber using a valve system and injected into the mold cavity for molding into a part. A feed tube may extend from the hot chamber to the valve system. The valve system may use gravity or pressure from a pump to meter a volume of molten alloy. In another case, the valve system may include a plunger and a shot sleeve for injecting alloy into the mold. In one embodiment, the plunger itself meters a volume of the alloy. The shot sleeve and plunger may optionally be heated.

Amorphous alloys may have unique combinations of properties—among them,high strength, corrosion resistance, low friction, and magneticproperties—due to their atomic structure. But, amorphous alloys must bequenched rapidly to achieve the amorphous structure, and there are fewforming/manufacturing processes that have been capable of producingamorphous alloy products that are technically and economically viable.

The die casting process has been used to cast amorphous alloys withmixed results. One of the challenges has been protecting the moltenalloy from the melt process all the way from the crucible to the moldcavity. Many amorphous alloys are highly reactive with oxygen and/ornitrogen while in the molten state. The reaction forms oxides whichbecome inclusions in the castings, resulting in reduced mechanicalproperties and surface imperfections.

To deal with the reactive nature of amorphous alloys, one approach hasbeen to use vertical die cast machines, in which the entire melt system,pouring system, dies and molds, and casting ejection/removal/handlingsystem are enclosed in a large vacuum chamber. Material feedstock isgenerally shuttled into the chamber through vacuum lock chambers, andthe cast parts are likewise shuttled out of the chamber through similarvacuum lock chambers. Generally an individual ingot is melted directlyin the ladle crucible for each shot. A limitation of vertical die castmachines is that cycle times tend to be long.

Horizontal die cast machines, which typically seal the die faces to eachother and evacuate only the mold cavity with vacuum once the dies areclosed, have also been used. One problem with such systems, however, isthat of isolating the melt system while the dies are open. Typically, a“cold shot chamber”, often just called a “shot sleeve”, connects withthe stationary die. A shot sleeve typically has an open port on the topthrough which the molten alloy is poured. The shot sleeve houses aplunger that retracts to open the port to receive the alloy, then pushesthe alloy toward the dies and into the mold cavity to form the casting.For reactive alloys, the cold chamber may be enclosed by a vacuumcavity, which also houses a crucible into which an ingot is fed for eachshot. However, while the dies are open (as is necessary to eject eachcasting), the plunger tip OD and shot sleeve ID are exposed to air (inparticular, oxygen and nitrogen) and atmospheric pressure. The only sealbetween atmosphere and the shot sleeve/crucible vacuum chamber is theplunger OD itself, yet the necessary small gap between the plunger ODand the shot sleeve ID allows atmosphere to leak past and into thevacuum chamber. Once the dies are again closed, the atmosphere in boththe mold cavity and the chamber must be drawn down to an acceptablevacuum level before melting of the next ingot can be initiated. Vacuumdrawdown time can contribute to excessively long cycle time when usinghorizontal die casting machines with reactive amorphous alloys.

The reactive nature of amorphous alloys, plus their relative highmelting temperatures, causes them to wet the iron-base alloys typicallyused in die casting, and in fact even to wet some ceramic materials.This can lead to the problem of the amorphous alloy “brazing” componentstogether, particularly if those components are below the solidustemperature of the alloy, and if the melt stays in contact with saidcomponents for any significant time duration. This makes it difficult touse components such as valves to isolate certain regions (in particular,those containing melt) of the die casting system from contact with air.

Another problem with either vertical or horizontal systems as describedis that an individual ingot is melted for each casting cycle. As such,the crucible must withstand repeated thermal cycles, which can causecrucibles breaks down and contribute contamination to the melt. Further,crucibles will typically eventually crack from thermal cycling. “Hotchambers”, which are crucibles or holding tanks that hold a largequantity of molten alloy and are maintained at a fairly constanttemperature, would seem to be a better solution, but with amorphousalloys hot chambers have other limitations.

Many amorphous alloys have a higher melting point, or liquidustemperature, than other alloys, such as those based on aluminum ormagnesium, that are commonly used in die casting. The liquidustemperatures of many are above the typical tempering temperature of thehigh-strength steels normally used in die casting machinery. At theseelevated temperatures, steels soften and lose much of their strength.For this reason, steels often cannot be used in continuous, prolongedcontact with molten amorphous alloys. For example, the iron-based hotchamber traditionally used with magnesium alloys is not used withamorphous alloys. The alloys, at or above their liquidus temperatures,react with iron-based materials. Elements from the iron-based materialscontaminate the melt and reduce the properties of the final castproduct. Further, degradation of the iron-based materials makes themwear rapidly and reduces their strength, preventing them from achievingtheir normal performance characteristics; for example, at thetemperature required to melt many amorphous alloys, a pump in aniron-based hot chamber cannot be expected to survive long, or togenerate as high a pressure as it would in its usual molten magnesiumenvironment.

Some of the issues given are particularly problematic when it comes todie casting components that require thin cross-sections and/or“cosmetic” (highly-polished) as-cast surface finishes. Oxidation,porosity, inclusions, flow-related defects such as flow lines, laps, andcold shuts are unacceptable defects in such products.

Traditional die casting uses very high injection rates, with moltenfluid flow velocities of 30 m/sec to 50 m/sec to prevent the moltenalloy from cooling due to contact with the various passages that connectthe crucible to the mold cavity. However, the turbulence induced by suchvelocities can cause void pockets and particulates from localizedsolidification of bubbles and spray droplets. If these defects “freeze”,or solidify, upon contact with the mold cavity, unacceptable defects arelikely to result.

Further, solidified particulates are difficult to force through smallcross-sections of molds, limiting designers' abilities to makelightweight components.

Turbulence can be eliminated by reducing the flow rate of the moltenalloy, but then premature solidification is more likely to occur due toextended contact duration with the internal passages.

So, what is needed for effectively die casting reactive amorphous alloysis a system that:

-   -   1. Melts the alloy, and transports it, in containers/passages        that do not contaminate the molten alloy by:        -   a. Avoiding thermal cycling which would break down the            containers/passages        -   b. Using materials that will not wet or react with the alloy            at temperature    -   2. Maintains the temperature of the melt from the crucible to        the mold cavity at a sufficient level to:        -   a. Avoid any localized freezing that would introduce solid            or semi-solid particulates that would prevent flow in thin            sections or cause flow line artifacts, or surface/subsurface            imperfections in the cast part        -   b. Prevent the occurrence of weld lines/laps/cold shuts    -   3. Maintains the alloy in an inert atmosphere from melt all the        way through solidification in the mold. In particular, when the        dies are open, prevents air from entering through the opening in        the fixed die and making contact with the molten alloy.    -   4. Controls injection rates to prevent spraying/turbulence that        would cause porosity, flowline artifacts, and/or solidification        inclusion defects.    -   5. Meters a controlled shot volume to the mold cavity (or,        allows the melt to quickly retract from contact with anything        “cold” (i.e., less that solidus temperature) after each shot.    -   6. Preferably, moves the melt continuously upwards (i.e., fills        all passages from the bottom up) to prevent defects from melt        tumbling and waterfalling from being created at locations in the        flow path, and ultimately progressing into the casting and        solidifying as defects. (Note—this becomes less important—but        still not unimportant—as other means, such as items 2-4 above,        to manage melt behavior are utilized.)    -   7. Completes the injection process with high pressure to        minimize porosity, thereby maximizing strength properties and        cosmetic surface finish.    -   8. After dies are opened to eject the part, then closed,        re-establishes the inert atmosphere within a reasonable time        frame.

All of the concepts in this application offer the following advantages:

-   -   Allows use of dies which do not need to be enclosed in a large        vacuum chamber, also eliminating various vacuum shuttle ports.    -   Allows use of a large (not single-shot) hot chamber, eliminating        thermal cycling which has been a source of crucible breakdown        and resulting melt contamination.    -   Allows a high quality vacuum to be built up quickly in the mold        cavity before introducing the melt    -   Provides a means of sealing the melt system from exposure to the        atmosphere while the dies are open    -   Allow use of lower injection velocities        This Document Details Items that are Generally not Detailed in        Each Concept Document, Because they are Common to all.

The term “hot chamber” is used throughout. This is because in allconcepts the supply of molten metal can come directly from either:

-   -   A crucible or furnace which is continuously fed a new supply of        feedstock material (e.g., ingots, scrap, or raw materials), or    -   A holding tank, transfer tank, dosing tank, or dosing furnace        (i.e., a tank or container that holds multiple doses designed to        meter a certain dose or volume of molten material for each shot)        which is fed from a crucible or furnace, then transported to the        die cast machine

The concepts disclosed herein related to high-fidelity amorphous metalcasting as well as a method of using a hot thank, hot chamber, etc. toinject or to supply a machine that injects amorphous alloys.

Such concepts may, however, also be used in other methods likeinvestment casting, though die casting is generally referencedherethroughout.

The term “melt” is generally used as a noun, referring to the moltenalloy of which the casting itself will be made.

In the molten state, amorphous alloys are generally reactive with air.The reaction products prevent the end casting products from achievingcosmetic finishes, and may degrade their mechanical properties as well.Thus, the systems embodied by these concepts ensure that from the timethat the feedstock is melted, to the time that it has been injected andsolidified in the mold cavity, it is never exposed to air, but ratherexposed only to an inert environment. Exemplary inert environmentsinclude, but are not limited to, vacuum and argon gas.

Amorphous alloys in the molten state are also generally reactive withmany other metals, including iron. The duration of exposure is a factorin the extent of reaction. Thus, in any area of the system in which themelt is in contact with an element of the system for more than a fewseconds, that element should be made of a material that does not reactwith the melt. In general, certain ceramics are the best material choicefor this purpose.

Ceramic components such as the feed tube(s) going from the crucible/hottank to the shot chamber or valve, and the valve and valve bodiesthemselves, need to be heated as a minimum, above the solidustemperature of the alloy being cast. Induction heating will not workwith ceramics, so the best method is believed to be resistive heating.Resistive heating may be used in conjunction with thermocouples in afeedback loop to achieve precise temperature control.

In the molten state, amorphous alloys exhibit fluid rheologicalproperties that vary as a function of temperature. It is thus importantto control the temperature of the melt being injected, at variouslocations throughout the system, by controlling the temperature of thesurfaces with which the melt comes into contact. Controlling melttemperature thus is a method to prevent defects in the final castingproduct by preventing premature solidification, as well as ensuring thatthe mold cavity is able to completely fill before the melt solidifies.These concepts mention specific heating requirements that are unique toeach concept. However, die heating and cooling are barely, if at all,mentioned in these concepts because, to some extent, they considered tobe part of each concept. This statement applies to all concepts: Theextent of die heating and cooling may vary depending on the efficiencyof the various systems in delivering melt at the proper temperature andspeed to the mold cavity. Dies, the mold cavity, and various componentssuch as sprue bushings may be heated with fluids such as oil or heattransfer fluids, or with inductive or resistive electrical heatingelements. Cooling may be accomplished with oils, water, or water-basedheat transfer fluids. Depending on the needs at specific locationswithin the system, components may be continuously heated, continuouslycooled, neither actively heated or cooled, or alternately heated andcooled with each cycle.

Each system is presumed to be capable of using recycled cast materialwith minimal reprocessing by feeding it into the crucible.

In some of these concepts, where a concept requires a pump in the hotchamber, EM pumps are cited as the preferred embodiment. However, ineach case, the function of the pump is only to transfer the molten alloyto the PMV, shot sleeve, or mold cavity; the pump is not required togenerate high pressure. (The fact that the final high pressure squeezecomes from another source is one reason that we think we can get awaywith old school, pump-in-hot-chamber technology with these high-meltingtemperature alloys.) We believe that EM pumps will work, or can be madeto work with our alloys because they work with aluminum, and ourliquidus temperatures aren't too higher than that of aluminum. However,if EM pumps won't work, ceramic centrifugal pumps or piston/sleevesubmerged pumps, either made of ceramic materials, should work.

DEFINITIONS

“Biscuit”—the portion of a casting that is where the melt first enteredthe mold cavity. The biscuit is waste material that is trimmed off thecasting after its ejection from the mold cavity. The function of thebiscuit is to serve as a sink for shrinkage in the critical areas of thecasting, and to serve as a collector for gas bubbles and oxidizedparticulates that tend to be entrained in the last bit of melt to beinjected into the die.

Feed tube—a tube connecting, and feeding melt between, a hot chamber ananother element (e.g., a cold shot chamber).

Dies—two large plates that clamp together and provide the force requiredto constrain the pressurized melt during injection. Dies generallycontain mold cavity inserts. Die casting machines generally have amoving, or ejector, die, and a stationary, or cover, die. The melt isgenerally first injected through the cover die. Dies must come together(close) to allow the melt to be injected into the mold cavity, andseparate (open) to eject the solidified casting.

Mold cavity—the internal, formed surfaces within the dies that createthe exterior surface of the finished casting itself. The mold cavity isgenerally constructed of mold inserts that are affixed to the dies, aswell as various components such as cores and sliders that are used tocreate certain features.

Inert gas—a gas, or mixture of gases, that has little or no tendency toreact chemically with the melt.

Cold chamber, or cold shot chamber—a piston-and-cylinder arrangementthat injects melt into the mold cavity at high pressure. The coldchamber is generally maintained at a nominal temperature well below thatof the melt itself.

Shot sleeve—the cylinder that houses the plunger. A shot sleevegenerally has a fill port into which melt is poured. As the melt isrammed into the mold cavity by the plunger, the shot sleeve mustwithstand significant pressure.

Plunger—the piston in the shot sleeve.

Shot—a specific volume of melt that is injected into the mold cavity toform the casting.

Waterfalling—a condition in which melt flows down a surface, oftenleaving artifacts such as gas bubbles and solidification-inducedparticulates and layers in the casting.

“Advance”—movement of a plunger, pump, or melt itself that causes meltto progress toward the mold cavity

“Retract”—movement of a plunger, pump, or melt itself that causes meltto progress away from the mold cavity

“Metering”—pumping, or allow the transfer, of a predetermined volume ofmelt (a “shot”) that will completely fill the mold cavity with acalculated, small amount of excess

Define and give values for solidus and liquidus temperature

System Objectives

-   -   Low melt fluid velocities (no turbulence)    -   No gas bubble entrapment in casting    -   No reaction of melt with air or container (hot chamber, pump,        etc.) materials    -   “Cosmetic” finish on certain surfaces (defect free—no surface or        internal defects, generally pure and clean)

The concepts disclosed herein relate to atmospheric control (includingsealing) and mechanical devices necessary to make the systems andmethods work. Further aspects include maintaining a melt temperaturethroughout the cycle, injecting the melt at a (slower) rate to reduceturbulence and flow-related spraying, reducing cycle time (e.g., below30 seconds), e.g., reducing the time to at or around 15 seconds, therebyincreasing efficiency in terms of costs and the die casting process, andisolating melt from the atmosphere during the processes.

Where the atmosphere in the mold cavity is inert gas, that gas may beused at roughly atmospheric pressure, or its pressure may be increasedto provide “counter pressure”—that is, pressure greater than atmosphericpressure. One benefit of counter pressure is that it may be used tocontrol the properties of the advancing front of melt. The tendency ofthe melt to “wet” the mold cavity surface is affected by counterpressure. Another benefit of counter pressure is that to the extent thatthere are any gas bubbles in the melt, counter pressure will compressthose bubbles to a smaller size. Further, flow-induces effect such ascavitation, which can cause damage to the mold cavity surfaces and leavedefects in the casting, are suppressed by counter pressure. Each conceptdisclosure has a table that identifies whether use of counter pressureis a viable option with the given configurations.

The concepts disclosed herewith include different ways of metering eachshot for each casting that is made. In some of them it has a meteringpump. In others the plunger tip itself does the metering. In othersthere's a couple of valves that do the metering. Each describes a way ofcontrolling how much volume is taken out of the hot chamber and put intothe shot sleeve for each casting.

Generally, in each concept the melt never sees, never is in contact withany metal that's at a lower temperature than its solidest temperatureand never in contact with any atmosphere that it would react to from thetime that it's molten until the time that it solidifies in the die, inthe mold cavity. The material is never being transferred to a coldchamber per se—or a cold shot sleeve. It gets all the way to the cavityin an environment that is heated. Further, it may be transferred inprotected environment (e.g., vacuum) to the die cavity.

In some cases parts are lined with ceramic material.

Summary of Overall System Concepts A Through C for Die Casting ofAmorphous Metals

Concepts A through C all involve a valve means adjacent to the cover dieto seal the melt supply/hot chamber from exposure to air while the diesare open. The valving mechanisms require mating contact between twocomponents, and when they come into contact, there is initially moltenmetal between them. There is a danger that the molten metal may solidifyand “braze” the two together; thus, it is necessary to ensure that anymolten metal between the two never drops below its solidus temperature.In these concepts, then, the conduits between the hot chamber and thecover die are all heated above the solidus temperature; inner surfaces,at least, are ceramic to prevent the melt from reacting with thosesurfaces. The plunger and shot chamber (where used) are also heated, andmade of, or coated with, ceramic.

In a conventional “cold” shot chamber system, the plunger and shotsleeve are generally steel, and thus their exposure to melt must be of avery short duration. This limits the orientations that can be used, andgenerally dictates that the melt be poured into an opening on the topside of the shot sleeve. In Concepts A-C, since the shot sleeve andplunger are by necessity heated, and constructed of ceramic, theserequirements do not exist. So, a variety of plunger and feedorientations are possible. For example, a plunger may be vertical,pointed up, and the feed port in the shot sleeve may be in constantcontact with the melt. This may lead to advantages such as quicker cycletimes and less likelihood of turbulent flow of melt into the shotchamber.

Concept A:

Melt is supplied by a hot chamber, protected by an inert atmosphere fromcontact with air, to a plunger that is housed in a shot chamber. Inaddition to driving the melt into the mold cavity, the plunger has twonovel functions, 1.) to meter the volume of melt being injected and 2.)to seal the hot chamber/gooseneck from intrusion by air while the diesare open. The melt may be driven from the hot chamber to the plunger bya pump, by gravity in versions in which the pressure differentialbetween the hot chamber and the mold cavity is either positive or zero,or by gas pressure in versions in which a positive pressure differentialexists between the hot chamber and the mold cavity. Squeeze pin(s) arenecessary to provide the desired high pressure at the end of theinjection cycle. There are two possible combinations of atmosphericprotection for the melt:

Concept Hot chamber atmosphere Die atmosphere A1 Vacuum Vacuum A2 Inertgas Vacuum

The design of the plunger/metering valve requires gravity to transferthe melt from the metering chamber to the shot chamber. Thus, theplunger axis must be in orientations 1 or 2 (see definitions at the endof this document) as defined herein. This requirement also limits theinert atmosphere in the mold cavity to vacuum only.

Concept B:

Melt is supplied by a hot chamber, protected by an inert atmosphere.There is no plunger; melt is driven into the mold cavity by either apump, or (as in Concept A, depending on whether pressure differentialconditions allow these methods) by gravity or gas pressure. A valveallows the melt to enter the mold cavity once the dies are closed andthe proper inert atmosphere has been established in the mold cavity; thevalve closes prior to the dies opening to protect the melt in the hotchamber/gooseneck from reaction with air. In one version, the pump maymeter the melt volume injected into the mold cavity; in other versions,vacuum/gas shutoff valves in the die(s) are relied upon to control themelt volume. Squeeze pin(s) are necessary to provide the desired highpressure at the end of the injection cycle; the valve may be used towithstand the pressure generated by the squeeze pins. The inertatmosphere combinations are similar to those of Concept A, but use ofinert gas in the mold cavity is also possible.

Concept Hot chamber atmosphere Die atmosphere B1 Vacuum Vacuum B2 Inertgas Vacuum B3 Inert gas Inert gas B4 Vacuum Inert gas

Concept C:

As in Concept A, melt is supplied by a hot chamber, protected by aninert atmosphere, to a plunger that is housed in a shot chamber. In thiscase, the plunger does not meter the melt, but does have a tip thatseals and functions as a valve to protect the melt from exposure to airwhile the dies are open. Again, squeeze pins are needed to provide highpressure. The feed options and inert atmosphere combinations are thesame as in Concept B.

C1 Vacuum Vacuum C2 Inert gas Vacuum C3 Inert gas Inert gas C4 VacuumInert gas

The concepts above, and various feed and orientation options areoutlined in more detail in the table below:

Concept A: Shot Metered by Combined Plunger/Metering Valve (PMV) SystemDescription

-   -   The supply source of molten alloy (“the melt”) is a hot chamber        (i.e., crucible or holding furnace containing a large volume        (more than one shot) of melt).    -   The melt in the hot chamber is protected from reacting with        oxygen in the atmosphere by blanketing the melt with a constant        inert (vacuum or inert gas) environment.    -   After each casting solidifies and the dies open to eject the        casting, the dies close and the mold cavity is purged by vacuum        (e.g., to get rid of oxygen and nitrogen molecules that will and        react with the melt).    -   To prevent air from making contact with the melt in the feed        tube/hot chamber while the dies are open, the plunger/metering        valve (PMV) has a tip that seals on a mating valve seat in the        cover die.    -   The PMV also has a “waist” section that functions as a metering        chamber to meter an exact shot size when in the “fill” position.    -   The PMV is actuated to 4 positions (see graphics on last page):        -   1. Sealing vacuum against atmospheric pressure when the dies            are open        -   2. Filling the metering chamber        -   3. Dumping melt from the metering chamber to the shot            chamber        -   4. Driving the melt into the mold cavity.    -   The PMV and metering/shot chamber axis are inclined at an angle        with respect to horizontal (in the example shown, 45 degrees) to        cause the melt to transfer by gravity from the metering chamber        to the shot chamber.    -   The feed tube axis is preferably connected to the bottom side of        the shot chamber so that the melt feeds from the bottom up, to        minimize turbulence.    -   The metering chamber may be supplied with melt from the hot        chamber by various means, including gravity, gas differential        pressure, or a pump.    -   In the case of a pump, two basic pump versions may be used. The        first is a non-metering, or non-positive displacement, pump;        that is, it does not displace a specific or known amount of        fluid. It merely pushes fluid (i.e., melt) upon command until it        is shut off. Low pressure pumps such as electromagnetic (EM)        pumps or vane pumps are acceptable methods. In Concept A it is        not necessary for the pump to meter the volume of melt, because        the PMV performs that function.    -   Alternatively, a positive-displacement pump such as a plunger        pump may be used (although its metering functionality would be        redundant). In this case, the pump will push fluid until the PMV        metering chamber is full, then hold position until the PMV        strokes and injects that fluid into the mold cavity. Ideally        such a pump will have a check valve, so that a supply of melt        remains in the feed tube while the plunger retracts and sucks in        more melt in preparation for the next injection cycle.    -   It is advantageous for all the elements mentioned above to be:        -   Made of ceramic to avoid wetting and reaction to/degradation            from the melt        -   (As opposed to a tradition “cold chamber system”) heated to            a constant temperature (above the solidus temperature of the            melt) to:            -   Minimize thermal cycling that could break down the                ceramic and thereby contaminate the melt            -   Prevent the melt from locally solidifying at the wall                boundaries when passing through these elements. This is                particularly an issue due to the injection velocities                used, which will be much lower than those used in                conventional high pressure die casting.    -   The feed tube and hot chamber linings, and hot chamber pump        materials may be made of various ceramic materials including        fused silica, aluminum oxide, aluminum titanate, zirconium        oxide, and magnesium oxide; specific examples are Al₂O₃+MgO and        Al₂O₃+SiO₂ ceramics.    -   The PMV protects the melt while the dies are open, and also        allows a high quality vacuum to be built up in the dies in the        interval while they are closed but before the valve is opened.        The best way to achieve a vacuum seal in this situation is with        a ceramic-to-ceramic face seal (in this case on conical faces)        as opposed to a small-gap (leaky) seal as would be typical when        sealing between the OD of the plunger and the ID of the shot        sleeve (as has been tried in the past).    -   It is critical that the melt does not solidify in the PMV area.        The melt between the PMV tip and mating valve seat must be        heated to above its solidus temperature to prevent the melt from        solidifying between the sealing faces of each and “brazing”        these together. One method is to resistively heat at least one,        or preferably both, of the PMV tip and mating shot chamber valve        seat. The preferred method is to inductively heat the melt alone        using an induction coil surrounding the valve seat. In this case        the valve and valve seat are made from a ceramic material such        as fused silica, which has low thermal and electrical        conductivity (“low dielectric loss factor”); thus only the melt        and not the valve and valve seat themselves will be heated by        the induction coil.    -   The best ceramic valve material is considered to be fused        silica. Other options may include aluminum oxide, and aluminum        titanate. PMV stroke is monitored by a displacement sensor. In        the event that a metering/positive displacement pump is used, a        control signal must be sent to the pump to shut it off when PMV        displacement reaches Position 3 (such that the feed tube is shut        off by the PMV).    -   Once the melt reaches the shot chamber, it is driven into the        mold cavity by a controlled plunger speed to eliminate        turbulence which could cause imperfections in the finished        casting.    -   The PMV must bottom out at the end of its stroke to provide        vacuum sealing when the dies are opened. As such, the PMV cannot        be relied upon to provide a predictable final pressure to the        mold cavity, because the exact volume injected may vary slightly        from shot to shot. Final pressure can be provided by squeeze        pins. These could be driven by hydraulic pressure, or simply be        spring-loaded to provide a predetermined pressure. The latter        case is preferred, because it would not be necessary for the        control system to either anticipate, or use sensing means to        determine, the correct instant at which to activate the squeeze        pins. In the latter case, the PMV would provide the source of        pressure, and the squeeze pins would regulate that pressure once        the die is full (similar to pressure relief valves). In this        case, the metered melt volume would be sized such that when the        plunger bottoms out, there is a small excess volume of melt in        the mold cavity to ensure that the squeeze pins will have to be        depressed to compensate for that excess volume.

An example injection cycle for a non-metering pump is as follows:

Die position PMV Position Action Feed tube Pump Open 1 (sealed Ejectingprevious Shut off Off against die) cast part Closed 2 (fully Fillingplunger Open to On retracted) metering chamber; metering pulling vacuumon die chamber Closed 3 (melt Transferring melt from Shut off Ontransfer) metering chamber to shot chamber Closed 4 (moving from Drivingmelt into die Shut off On 3 to 1) cavity at controlled rate Closed 1Allowing melt in die Shut off On to solidify Open 1 (sealed Eject castpart Shut off On against die)

In the example above, since the pump is non-metering, it may be left oncontinuously so that melt is always in contact with the shot sleeve feedport. The same is true of gravity or gas pressure feed.

Discussion

The advantages of this system are:

-   -   Allows use of a large (not single-shot) crucible/hot tank,        eliminating thermal cycling which has been a source of crucible        breakdown and resulting melt contamination    -   Provides a means of sealing the melt system from exposure to the        atmosphere while the dies are open    -   Allows a high quality vacuum to be built up quickly in the mold        cavity before introducing the melt    -   Allows use of dies which do not need to be enclosed in a large        vacuum chamber, also eliminating various vacuum shuttle ports    -   Provides a means of metering an exact shot volume to the die    -   May be used with either vacuum/inert gas for protecting the melt        in the hot chamber from exposure to atmosphere.

A potential drawback of this system is that the requirements on the PMVare more demanding than they are on most other systems/elements; the PMVmust hold vacuum, yet also be exposed to molten alloy flowing past it,and must be maintained at above the alloy solidus temperature.

Because of the need for a valve that is exposed to melt near the supplyand also must hold vacuum, this disclosed approach has not beenattempted or known. (Most vacuum valves in vacuum die cast systems areat the top of the die, at the last point reached by the inflowing melt,and as such are exposed to much lower temperature.

The overall system concept is shown below in Figures A1 and A2(sectional views):

In accordance with another embodiment, inert gas is used in the cruciblealong with vacuum in the die (see A2 below). A2 is mechanically similarto Concept A1; the only differences pertain to atmosphere control. Forexample, the crucible/hot chamber is under constant pressure from aninert gas, such as argon. In addition to the previously notedadvantages, due to the positive pressure in the crucible/hot tank, A2does not rely heavily on the extent to which the PMV can hold vacuum.

The PMV must hold vacuum in the die, yet also be exposed to molten alloyflowing past it, and must be maintained at slightly above the alloyliquidus temperature.

In another embodiment, an inert gas is in the crucible, still vacuum inthe die, but the melt is driven by gas pressure from the crucible and apump is not used (see Figure below). Here, this concept is using thepressure of the inert gas to drive melt into that shot sleeve meteringchamber or valve. So, while the above two embodiments have anon-metering pump in the crucible, e.g., this embodiment—with no pump inthe crucible—uses the inert gas pressure in the crucible (which would beslightly higher than the atmosphere—e.g., 15 PSI absolute) to drive themelt into the metering chamber in the plunger. The pressure differencein the crucible (just over atmospheric, at about 15 psia) and that inthe vacuum-evacuated mold cavity (essentially zero psia) pushes the meltinto the PMV metering chamber.

-   -   In this embodiment, when PMV displacement reaches Position 3        (see Figure later below), such that the feed tube is shut off by        the PMV, there is no mechanism to relieve the pressure driving        the fluid up the feed tube. As such, the entire feed tube must        be heated to above the liquidus temperature to prevent the        molten alloy therein from solidifying.

In yet another embodiment, an inert gas is in the hot chamber but nowinstead of having vacuum in the die, an inert gas is introduced into thedie as a different means of having atmospheric control. This gas may beused for what we call counter pressure. That is, there is a positivepressure in the die and the gas is pushing against that; this positivepressure has some beneficial effects as far as the front of the melt isconcerned.

The front of the melt is the first part of the melt that is advancinginto the mold cavity. So counter pressure has some effects on thesurface tension of the melt, and affects the way that melt frontbehaves. It makes it behave better with respect to not breaking up andnot spraying as it comes out of the gates, for example, and not gettingturbulent.

This inert gas introduced into the mold cavity may or may not becontrolled as counter pressure, however. But it's possible it may bequicker to get rid of oxygen and nitrogen in the mold cavity by firstapplying vacuum, then applying an inert gas and then possibly vacuumagain, then inert gas again. For example, the first time vacuum isapplied to the die cavity, say, 99% of the oxygen and nitrogen areremoved, but then to get the rest of it out, one may either keep onpulling vacuum to get that last 1% out, or quickly fill that vacuumvolume with inert gas, and it still has 1% air in it and 99% inert gas,then suck out that inert gas and oxygen combination again. This mayreduce it down to 0.1% oxygen and nitrogen, if you apply the same levelof vacuum to it.

In Summary, in addition to the previously noted mechanical featuresreferenced above (e.g., see A2), this embodiment describes the use ofinert gas and positive pressure in the mold cavity)

The die is purged by vacuum first, then filled with inert gas (e.g.,argon) to provide counter pressure during injection to help preventturbulence and breakdown of the melt front.

The die fill process may involve a single step each of vacuum and inertgas fill, or multiple steps such as vacuum/inert gasfill/re-vacuum/re-inert gas fill to further reduce the oxygen level inthe mold cavity.

As with Concepts A1 and A2, but unlike the third, a pump pushes fluidupon command to the metering chamber; a low pressure pump such as an EMpump is an acceptable method. In this embodiment it is not necessary forthe pump to meter the volume of melt, because the PMV performs thatfunction.

It can introduce a positive pressure to prevent those bubbles from everforming to begin with which is also an advantage.

This system may require additional overflow areas for the counterpressure gas, and/or pressure relief valves that limit the maximumpressure and vent the inert gas back to the inert gas source to recycleit.

Allows a high quality vacuum and positively-pressured inert gasatmosphere to be built up in the mold cavity before introducing themelt.

In one embodiment, the overall concept is to have a plunger that metersthe shots, so the plunger itself has two functions. It pushes the meltinto the mold cavity but it also meters the shot itself so it allows useof any kind of pump in the hot chamber. This disclosure uses amorphousmetals with the hot chamber concept, which has never been done before,and it does solve some problems. For example, it solves that problem ofrepeated thermal cycling and individual one-shot melts.

In the figure shown in Concept A1, we're pumping some melt to the shotchamber, but because we're no longer melting an individual ingot whichis perfectly sized to the size of shot that we need, we now use a methodof metering the amount of melt that is given to the shot chamber of theshot sleeve. In this case, the plunger itself is that metering method.

As shown in the figures above and below, the angle of the plunger isshown at about 45 degrees. The reason for that is with this particularconcept, it requires gravity so that once the metering chamber is full,then the plunger is put in a different position that requires gravity toallow the melt to progress down to the next session of the chamber(gravity feed). So that's the reason for the inclined plunger. The pumpin this case it can be something like an EM (electromagnetic) pump,which in this case would not need to have its own metering. Pumps can beused in conjunction with a sensor such as an EM sensor where you controlthe current that's sent to the pump based on what the sensor says thevolume is or has been. So those two things in combination can be ametering pump. But a metering pump can be just used in an on/off mode tosupply a chamber as long as that chamber has a fixed volume.

The biscuit would be part of the casting that's injected. Theconfiguration as shown is a draft angle that's easily ejectable. Soinstead of having a conventional sort of round biscuit with a little bitof a draft angle on the sides of it, it would be shaped a little lesslike that so that it's ejectable.

In Concept A1, it's all vacuum system and so there wouldn't be air, andthat melt would find its own level and the plunger would approach ituntil just hits melt and it would start pushing it in.

In an embodiment, that there can be a plurality of rotating circulardies such as that pumping and flowing it simply keeps going onconstantly.

Squeeze pins are also shown in the figures. Squeeze pins in die castingare used to increase the pressure generally at the end of thecycle—e.g., at the end of the injection cycle. Basically they arepiston-like devices that either extend into the mold cavity a little bitor can be forced by the melt to retract into their bores a little bit.The same pins can be used as ejector pins, so once the casting hassolidified and once the die is open and the casting is ready to beejected, the squeeze pins are used to push the casting back out. Squeezepins can perform that dual role.

In one embodiment, in the bore that squeeze pin resides in, a spring inthat bore pushes on the squeeze pin to form a spring-loaded pin. In someembodiments, by putting a preload on it, the plunger is made to retractwith a predetermined pressure.

Position 1 shows an angled shot chamber and the plunger. The tube thatbranches off down to the lower right is the feed tube that connects withthe hot chamber itself (the source of molten alloy). In position 1, theplunger tip seals off the hot chamber. All these components aremaintained above the liquidus temperature of the alloy because when thisplunger tip is pressed against that ceramic seat, we don't want thealloy to serve as a brazing material and braze the plunger tip to theseat. So it is maintained above the solidus temperature. Also in theposition 1 shown, the dies are open and the plunger tip itself is actingas a valve to seal everything else—everything upstream of that if youwill—from the atmosphere. Then once the dies are closed and we havepulled a vacuum on the dies, the plunger is pulled back to position 2,which is the fill position.

In position 2 there's annular sealing around the OD of the plunger—thatis, there is a very small gap between the plunger OD and the shot sleeveID that functions as a seal—and so that volume shown there is going todefine the metering volume. So in position 2 the pump in the hot chamberis actuated to fill that volume with melt. Once it fills, which willjust take a fraction of a second, we move on to position 3.

In position 3, the large OD of the plunger has closed off the feed tubethat goes down to the hot chamber. Now the volume that was in thatannular area around that neckdown area of the plunger, it's now able togravity feed past the plunger tip and into the mold area—that is, intothat biscuit area.

Then finally in position 4, once we know that all the melt hasgravity-fed past that plunger tip empirically; (e.g., based on apredetermined amount of time, e.g., 0.05 sec)—then the plunger isadvanced. Once the plunger enters that final diameter within the shotsleeve, then it becomes a piston instead of a valve and it is drivenfurther forward. Now this is where the squeeze pins may come into play.If you just push that plunger tip all the way until it bottomed out onthe mating valve seat, if then the fluid volume that was in that shotwas a little bit low, the pressure in the die cavity won't build up. Onthe other hand, if it was a little bit high, the plunger tip wouldn't beable to stroke fully and seal on the valve seat. Thus, the squeeze pinsmay be employed to compensate for any differences in volume. As such,they could be simply preloaded by a spring, or they could be preloadedhydraulically or pneumatically to a certain pressure. The key is thatthey are able to be pushed in by the pressure that the plunger generateswhen it bottoms out on the seat, and compensate for any variation involume.

In yet another embodiment, no plunger and no pump are provided. Instead,it has just a valve that is right next to the biscuit—that is, rightnext to the casting. This valve is simply open and shut, so there's asource of pressure. That source of pressure is the pressuredifferential. There's a higher pressure in the hot chamber than there isin the die cavity because one has inert gas, the other has vacuum in it.

For example, melt is drawn to the mold cavity by the pressure differencein the crucible (just over atmospheric, at about 15 psia) and that inthe vacuum-evacuated mold cavity (essentially zero psia).

To isolate the crucible/hot tank from contamination by the atmospherewhen the dies are open, there is a valve adjacent to the biscuit.

Unlike the previous concepts, there is no ability to meter the shot. Thevalve is simply left open until the mold cavity is full.

After the mold cavity is full, the valve is shut, and shortly thereafterhydraulically-driven squeeze pins are to be activated to increase thefinal mold pressure. The purpose of increasing pressure is to minimizeporosity in the casting, and in doing so, increase mechanical propertiesand improve the surface finish of the casting. The valve, since it isnot a plunger per se, cannot generate this pressure, but neverthelessmust withstand it.

-   -   In particular, at least one, or preferably both, of the valve        and the mating valve seat, must be heated to above the liquidus        temperature to prevent the melt from solidifying between the        sealing faces of each and “brazing” these together.    -   There is no mechanism to relieve the pressure driving the fluid        up the feed tube. As such, the entire feed tube must be held at        a temperature above the liquidus (or at least solidus)        temperature to prevent the molten alloy therein from        solidifying. Roughly the same temperature as that of the melt in        the crucible/hot tank would be ideal.

The injection cycle is as follows:

Die Valve position Position Action Feed tube Pump Open Closed Ejectingprevious cast part Shut off from n/a mold cavity Closed Closed Pullingvacuum on die Shut off from n/a mold cavity Closed Open Transferringmelt from Connected to n/a crucible/hot tank to mold mold cavity cavityClosed Closed Activating squeeze pins to Shut off from n/a increasepressure in mold mold cavity cavity Closed Closed Allowing melt in dieto Shut off from n/a solidify mold cavity Open 1 (closed) Eject castpart Shut off from n/a atmosphere

Discussion

The advantages of this system are:

-   -   Allows use of a large (not single-shot) crucible/hot tank,        eliminating thermal cycling which has been a source of crucible        breakdown and resulting melt contamination    -   Provides a means of sealing the melt system from exposure to the        atmosphere while the dies are open, but due to the positive        pressure in the crucible/hot tank, does not rely as heavily as        Concept A1 on the extent to which the PMV can hold vacuum    -   Allows a high quality vacuum to be built up in the mold cavity        before introducing the melt    -   Allows use of dies which do not need to be enclosed in a large        vacuum chamber, also eliminating various vacuum shuttle ports    -   This concept is simpler that other concepts in that it does not        require a pump, and the valve actuation may be somewhat simpler        than that of the PMV. For example, its speed does not have to be        controlled. Further, it only has to actuate to two positions        (fully open and fully shut), so there is no need for a stroke        sensor or high-speed feedback control loop. Thus, its control        system requirements are simpler.

As with previous concepts, a potential drawback of this system is thatthe requirements on the valve are more demanding than they are on mostother systems/elements; the valve must hold vacuum in the die, yet alsobe exposed to molten alloy flowing past it, and must be maintained atslightly above the alloy liquidus temperature.

There are other potential drawbacks are unique to this embodiment(illustrated as Concept 5 below). One is that since the melt volume issimply drawn in by vacuum, it is not positively controlled/metered.Also, the fill rate is not controlled as it is with a PMV or plungertype system, and may be too slow or too fast.

Such an approach is not known and has not been done before, probablybecause of the need for a valve that is exposed to melt near the supplyand also must hold vacuum. (Most vacuum valves in vacuum die castsystems are at the top of the die, at the last point reached by theinflowing melt, and as such are exposed to much lower temperature.)

The valve protects the melt while the dies are open, and also allows ahigh quality vacuum to be built up in the dies in the interval whilethey are closed but before the valve is opened. The best way to achievea vacuum seal in this situation is with a ceramic-to-ceramic face seal(in this case on conical faces) as opposed to a small-gap (leaky) sealas would be typical when sealing between the OD of the plunger and theID of the shot sleeve (as has been tried in the past).

It is critical that the melt does not solidify in the valve area. Thisis the reason that the valve is designed and oriented so that nointernal surfaces are horizontal (so that the melt cannot pool), andthat the valve must be maintained close to, or above, liquidustemperature. As such, all valve body internal surfaces and the valveitself must be a ceramic material which the melt will not wet.

The best ceramic material is considered to be zirconia. Other optionsmay include alumina, magnesia, and silica; specific examples areAl₂O₃+MgO and Al₂O₃+SiO₂ ceramics.

The overall system concept is shown below:

Concept B: Valve Adjacent to Mold Cavity (No Plunger) SystemDescription—

-   1) The supply source of molten alloy (“the melt”) is a hot chamber    (i.e., crucible or holding furnace containing a large volume (more    than one shot) of melt).-   2) The melt in the hot chamber is protected from reacting with    oxygen in the atmosphere by blanketing the melt with a constant    inert (vacuum or inert gas) environment.-   3) After each casting solidifies and the dies open to eject the    casting, the dies close and the mold cavity is purged by vacuum.-   4) This system does not use a plunger in a cold shot chamber to fill    the mold cavity. The mold cavity is filled by either:    -   a) A pressure differential, for example 1 to 2 bar, between the        gas pressure in the hot chamber, and the gas (or vacuum)        pressure in the mold cavity,    -   b) Gravity (i.e., the hot chamber is elevated as compared to the        mold cavity)    -   c) A pump in the hot chamber.-   5) To isolate the melt from contamination by the atmosphere when the    dies are open, there is a valve adjacent, and connecting, to the    mold cavity. In one embodiment, the valve may be adjacent to the    biscuit.-   6) The valve axis optimally is vertical (pointed upwards), or    between vertical and horizontal (also pointed upwards. The figure    below shows the axis oriented at 45 degrees. In the angled    orientation the shot chamber may be filled from the feed tube    through a port the low side of the shot chamber. This bottom-filling    configuration will cause a minimum of flow disturbance as the melt    enters the shot chamber. In the event that gas is used in the mold    cavity, either of these orientations ensures that gas is likely to    progress through the mold casting first, and exit the vacuum valves    at the top of the mold cavity, and thus reducing the possibility of    gas being trapped in the casting.-   7) A heated feed tube connects the hot chamber to the valve. During    operation, the feed tube is constantly full of melt.-   8) The feed tube axis is also optimally between vertical and    horizontal (shown vertical) to facilitate filling of the shot    chamber with a minimum of turbulence.-   9) There are at least three methods to meter the shot volume. One is    that the valve is simply left open until the mold cavity is full.    This concept will require gas/vacuum valve(s) that stop the inflow    of melt and hold squeeze pressure. Valves that stop the inflow of    melt are known in the art. The valve(s) may perform that function    by:    -   a) Freezing (solidifying) the melt (or chill block),    -   b) Shutting off the inflow of melt by inertia    -   c) Shutting off the inflow of melt by a solenoid,    -   d) Other means.-   10) Another method to meter pump volume is to use a metering pump to    deliver a precise volume to the mold cavity. An example may be a    plunger pump that delivers a specific volume for a known stroke    length.-   11) A third method is to use a non-positive-displacement pump in    conjunction with a flow measurement means, such as a flowline    sensor.-   12) In the case of a system that uses vacuum valves, the control    system may use temperature sensors for chill block valves, or    electrical contact or stroke sensors for inertia or solenoid valves,    to determine that the mold cavity is full. In the case of a system    that meters the pump volume, pump stroke or flow sensors may be used    to determine that the mold cavity is full.-   13) Immediately after the mold cavity is full, the control system    will shut the valve, and very shortly thereafter one or more squeeze    pins are be activated to increase the final mold pressure. The pump    itself may be then shut off. The squeeze pin(s) may be driven by    hydraulic, pneumatic, electrical, or mechanical means. A hydraulic    cylinder with the pressure controlled to produce a desired pressure    in the melt itself is an exemplary method. The purpose of increasing    pressure is to minimize porosity in the casting, and in doing so,    increase mechanical properties and improve the surface finish of the    casting. The valve, since it is not a plunger per se, cannot    generate this pressure, but nevertheless must withstand it.-   14) The melt between the valve tip and mating valve seat must be    heated to above its solidus temperature to prevent the melt from    solidifying between the sealing faces of each and “brazing” these    together. One method is to resistively heat at least one, or    preferably both, of the valve tip and mating valve seat. The    preferred method is to inductively heat the melt alone using an    induction coil surrounding the valve seat. In this case the valve    and valve seat are made from a ceramic material such as fused    silica, which has low thermal and electrical conductivity (“low    dielectrnc loss factor”); thus only the melt and not the valve and    valve seat themselves will be heated by the induction coil.-   15) It is advantageous for all the elements mentioned above to be:    -   a) Made of ceramic to avoid wetting and reaction to/degradation        from the melt    -   b) (As opposed to a tradition “cold chamber system”) heated to a        constant temperature above the solidus temperature of the melt        to:        -   i) Minimize thermal cycling that could break down the            ceramic and thereby contaminate the melt        -   ii) Prevent the melt from locally solidifying at the wall            boundaries when passing through these elements. This is            particularly an issue due to the injection velocities used,            which will be much lower than those used in conventional            high pressure die casting.-   16) It is not necessary to provide a mechanism to relieve the    pressure driving the fluid in the feed tube in accordance with an    embodiment. Shot volume metering will be the simplest, and the most    accurate, if the feed tube is always full of melt. As such, the    entire feed tube must be held at a temperature above the solidus    temperature of the melt to prevent the molten alloy therein from    solidifying. Roughly the same temperature as that of the melt in the    crucible/hot tank would be ideal.

An injection cycle for a non-metering pump is as follows:

Die Valve position Position Action Feed tube Pump Open Closed Ejectingprevious Shut off from On, or holding cast part mold cavity ClosedClosed Pulling vacuum Shut off from On, or holding on die mold cavityClosed Open Transferring melt Connected to On from crucible/hot moldcavity tank to mold cavity Closed Closed Activating Shut off from On, orholding squeeze pins to mold cavity increase pressure in mold cavityClosed Closed Allowing melt in Shut off from On, or holding die tosolidify mold cavity Open 1 (closed) Eject cast part Shut off from On,or holding atmosphere

The table above gives the cycle for a pump; however, it is the same forgravity- or pressure-feed systems.

In accordance with embodiments, the pump may be an EM pump, centrifugalpump, piston pump, or any pump that can survive long term exposure inthe melt. High pressure is not a requirement.

It is useful to control the pump flow rate, but not necessary to meterthe shot. The valve may be simply left open until the mold cavity isfull.

Discussion

The advantages of this system are:

-   -   Allows use of a large (not single-shot) crucible/hot tank,        eliminating thermal cycling which has been a source of crucible        breakdown and resulting melt contamination    -   Provides a means of sealing the melt system from exposure to the        atmosphere while the dies are open    -   Allows a high quality vacuum to be built up in the mold cavity        before introducing the melt    -   Allows use of dies which do not need to be enclosed in a large        vacuum chamber, also eliminating various vacuum shuttle ports    -   It only has to actuate to two positions (fully open and fully        shut), so there is no need for a stroke sensor or high-speed        feedback control loop. Thus, its control system requirements are        simpler.    -   The flow rate into the mold cavity can be more controllable.        This is especially true if a positive displacement pump (e.g., a        piston pump) or EM pump is used.

As with previous concepts, a potential drawback of this system is thatthe requirements on the valve are more demanding than they are on mostother systems/elements; the valve must hold vacuum in the die, yet alsobe exposed to molten alloy flowing past it, and must be maintained atslightly above the alloy liquidus temperature.

Generally, this disclosed approach is not known, most likely because ofthe need for a valve that is exposed to melt near the supply and alsomust hold vacuum. (Most vacuum valves in vacuum die cast systems are atthe top of the die, at the last point reached by the inflowing melt, andas such are exposed to much lower temperature. Further, the melt doesnot go through the valve itself; rather, the valve control mechanism isdesigned to shut the valve just before the melt actually passes throughit.)

The valve protects the melt while the dies are open, and also allows ahigh quality vacuum to be built up in the dies in the interval whilethey are closed but before the valve is opened. The best way to achievea vacuum seal in this situation is with a ceramic-to-ceramic face seal(in this case on conical faces) as opposed to a small-gap (leaky) sealas would be typical when sealing between the OD of the plunger and theID of the shot sleeve (as has been tried in the past).

It is critical that the melt does not solidify in the valve area. Thisis the reason that the valve must be maintained close to, or above,liquidus temperature.

The best ceramic valve material is considered to be fused silica. Otheroptions may include aluminum oxide, and aluminum titanate. The feed tubeand hot chamber linings, and hot chamber pump materials may be made ofvarious ceramic materials including fused silica, aluminum oxide,aluminum titanate, zirconium oxide, and magnesium oxide; specificexamples are Al₂O₃+MgO and Al₂O₃+SiO₂ ceramics.

The overall system concept is shown below:

The above “Concept B2” shows an inert gas in crucible/hot tank, withmelt driven into mold cavity by a pump, and with a valve to isolatecrucible/hot tank from atmosphere while dies are open.

In the above illustrated Concept B2 there is no shot chamber or plungerbut instead the system has a valve in place of a plunger. This conceptprovides the melt from the hot chamber purely by pressure and the hotchamber is positively pressured. As described above, the mold cavity hasa vacuum so that once the valve is opened, the mold cavity fills basedon that pressure differential. Once the mold is full, the valve issimply shut and then the squeeze pins are actuated.

Traditionally hot chamber die casting is a relatively low pressureprocess because the pump is submerged in the hot chamber, and because atsuch a high temperature, the components of the pump can't take a wholelot of stress. It is typically a piston or plunger type pump. So the hotcamber process is typically relatively low pressure, say 500 to 1500 PSIor thereabout. But in the last 10-15 years, industry has realized,especially in aluminum products, that they need a high pressure squeezeto get high quality castings. So some known processes involve injectingwith the low pressure pump in the hot chamber, then freezing in thissprue area to provide essentially a valve (a stopper) there. As soon asthat sprue area has cooled, or actively cooled, as soon as that meltfreezes there but before the rest of the melt in the casting solidifies,they'll use squeeze pins to jack the pressure up (to maybe 10,000 PSI).It has been found that high pressurization makes a difference betweengetting good mechanical properties, and especially low porosityproperties, in castings, and getting bad properties.

In this disclosure, the melt is introduced in the die cavity with a lowpressure gas differential but then once the cavity fills, we close thatvalve—that same valve that is used to isolate the hot chamber from theatmosphere with the die opening. So once the cavity is full, we closethat valve and activate the squeeze pins to increase the pressure in themelt in the mold cavity, before it solidifies. That's crucial to thisprocess.

In one embodiment, a metering pump is used instead of gas to drive themelt from the hot chamber into the die, into the mold cavity.

In another embodiment, a non-metering pump is used to drive the melt in.

In either case, vacuum valves in the mold cavity may apply vacuum to thecavity when fluid melt is not being pushed in, and then when the fluidhits those valves, the molten fluid, it freezes up quickly and basicallyseals off the cavity. At that point you can further apply pressure.

In one embodiment, the vacuum is in both the hot chamber and in the die,and inert gas is used in the hot chamber and vacuum in the die.

In another embodiment, the crucible/hot chamber is under a vacuumenvironment, but does not require an inert gas system.

Concept C: Plunger with Sealing Tip System Description

-   -   1. The supply source of molten alloy (“the melt”) is a hot        chamber (i.e., crucible or holding furnace containing a large        volume (more than one shot) of melt).    -   2. The melt in the hot chamber is protected from reacting with        oxygen in the atmosphere by blanketing the melt with a constant        inert (vacuum or inert gas) environment.    -   3. After each casting solidifies and the dies open to eject the        casting, the dies close and the mold cavity is purged by vacuum.    -   4. A plunger housed in a shot chamber drives the melt into the        mold cavity. Unlike conventional “cold chamber” die casting        systems, though, the plunger and shot sleeve are maintained        “hot” (i.e., above the solidus temperature of the melt).    -   5. The plunger tip serves as the valve that seals the shot        chamber and the feed tube/hot chamber from atmosphere when the        dies are open. The plunger tip seals on a mating valve seat in        the cover die.    -   6. The plunger is actuated to 3 positions (see graphics on last        page):        -   a. Sealing vacuum against atmospheric pressure when the dies            are open        -   b. Filling the shot chamber        -   c. Closing off the feed tube from the shot chamber and            driving the melt into the mold cavity.    -   7. The shot sleeve axis optimally is between vertical and        horizontal (shown at 45 degrees). In this range the shot chamber        may be filled from the feed tube through a port the low side of        the shot chamber. This bottom-filling configuration will cause a        minimum of flow disturbance as the melt enters the shot chamber.    -   8. The feed tube axis is also optimally between vertical and        horizontal (shown vertical) to facilitate filling of the shot        chamber with a minimum of turbulence.    -   9. The shot chamber may be supplied with melt from the hot        chamber by various means, including gravity, gas differential        pressure, or a pump.    -   10. In Concept B it is necessary to meter the volume of melt        delivered to the shot chamber.    -   11. In versions in which the feed of melt from the hot chamber        to the shot chamber is provided by gravity feed, gas pressure,        or non-positive displacement pump (e.g., EM or vane pumps), the        flow rate must be monitored (e.g., by an EM flow sensor).        Plunger movement and flow rate must be timed and controlled so        that the plunger seals off the feed tube port (Position 3 in the        figures below) when the correct volume of melt has been pumped        into the shot chamber.    -   12. Alternatively, the preferred configuration uses a        positive-displacement pump such as a plunger pump. In this case,        the pump, based on its piston area and stroke, will push a known        volume of melt, then hold position until the plunger strokes and        injects that melt into the mold cavity. Ideally such a pump will        have a check valve, so that a supply of melt remains in the feed        tube while the plunger retracts and sucks in more melt in        preparation for the next injection cycle.    -   13. It is advantageous for all the elements (valve seat, plunger        tip, etc.) mentioned above to be:        -   a. Made of ceramic to avoid wetting and reaction            to/degradation from the melt        -   b. (As opposed to a tradition “cold chamber system”) heated            to a constant temperature (above the solidus temperature of            the melt) to:            -   i. Minimize thermal cycling that could break down the                ceramic and thereby contaminate the melt            -   ii. Prevent the melt from locally solidifying at the                wall boundaries when passing through these elements.                This is particularly an issue due to the injection                velocities used, which will be much lower than those                used in conventional high pressure die casting.    -   14. The melt between the plunger tip and mating valve seat must        be heated to above its solidus temperature to prevent the melt        from solidifying between the sealing faces of each and “brazing”        these together. One method is to resistively heat at least one,        or preferably both, of the PMV tip and mating shot chamber valve        seat. The preferred method is to inductively heat the melt alone        using an induction coil surrounding the valve seat. In this case        the valve and valve seat are made from a ceramic material such        as fused silica, which has low thermal and electrical        conductivity (“low dielectric loss factor”); thus only the melt        and not the valve and valve seat themselves will be heated by        the induction coil.    -   15. Once the melt reaches the shot chamber, it is driven into        the mold cavity by a controlled plunger speed to eliminate        turbulence which could cause imperfections in the finished        casting.    -   16. The plunger tip must bottom out at the end of its stroke to        provide vacuum sealing when the dies are opened. As such, the        plunger cannot be relied upon to provide a predictable final        pressure to the mold cavity, because the exact volume injected        may vary slightly from shot to shot. Final pressure can be        provided by squeeze pins. These could be driven by hydraulic        pressure, or simply be spring-loaded to provide a predetermined        pressure. In the latter case, the plunger would provide the        source of pressure, and the squeeze pins would simply regulate        that pressure once the die is full (similar to pressure relief        valves). In this case, the metered melt volume would be sized        such that when the plunger bottoms out, there is a small excess        volume of melt in the mold cavity to ensure that the squeeze        pins will have to be depressed to compensate for that excess        volume.

The pump may be a metering pump, for example (i.e., a pump that deliversthe melt from the hot chamber to the plunger to the shot chamber, and iscapable of delivering a specific volume of melt).

An example injection cycle for a metering pump is as follows:

Die Plunger position Position Action Feed tube Pump Open 1 (sealedEjecting Shut off Intake stroke against die) previous cast part Closed 1(sealed Pulling vacuum Shut off Intake stroke against die) on moldcavity Closed 2 (fully Filling shot Open to shot Exhaust strokeretracted) chamber chamber Closed (moving from Driving melt Shut offHolding 3 to 1) into die cavity position at controlled rate Closed 1Allowing melt Shut off Holding in die to position solidify Open 1(sealed Eject cast Shut off Intake stroke against die) part

In the example above, since the pump is metering (i.e., positivedisplacement), it may be held in position while the plunger shot chamberis not filling, so that melt is always in contact with the shot sleevefeed port.

The various combinations of atmosphere and feed methods are shown in thetable below:

Discussion

The advantages of this system are:

-   -   Allows use of a large (not single-shot) hot chamber, eliminating        thermal cycling which has been a source of crucible breakdown        and resulting melt contamination    -   Provides a means of sealing the melt system from exposure to the        atmosphere while the dies are open    -   Allows a high quality vacuum to be built up quickly in the mold        cavity before introducing the melt    -   Allows use of dies which do not need to be enclosed in a large        vacuum chamber, also eliminating various vacuum shuttle ports    -   Provides a means of metering an exact shot volume to the die    -   May be used with either vacuum/inert gas for protecting the melt        in the hot chamber from exposure to atmosphere.

A potential drawback of this system is that the requirements on theplunger are more demanding than they are on most other systems/elements;the plunger tip must hold vacuum, yet also be exposed to the moltenalloy flowing past it, and must be maintained at above the alloy solidustemperature.

Because of the need for a valve that is exposed to melt near the supplyand also must hold vacuum this disclosed approach has not been attemptedor known. (Most vacuum valves in vacuum die cast systems are at the topof the die, at the last point reached by the inflowing melt, and as suchare exposed to much lower temperature.

The plunger tip, serving as a valve, protects the melt while the diesare open, and also allows a high quality vacuum to be built up in thedies in the interval while they are closed but before the valve isopened. The best way to achieve a vacuum seal in this situation is witha ceramic-to-ceramic face seal (in this case on conical faces) asopposed to a small-gap (leaky) seal as would be typical when sealingbetween the OD of the plunger and the ID of the shot sleeve (as has beentried in the past).

It is critical that the melt does not solidify in the plunger area. Thisis the reason that the plunger must be maintained close to, or above,liquidus temperature.

In the particular configuration shown, the plunger tip seals against aseparate valve seat. This seat is made of ceramic. A separate valve seatis considered to be the ideal configuration, as it may exhibit adifferent wear rate, or necessitate different material properties, thanthat of the shot sleeve. However, as the shot sleeve in this conceptmust also be either made of ceramic, or lined with ceramic, the valveseat alternatively could be formed integrally into the shot sleeve.

The best ceramic valve material is considered to be fused silica. Otheroptions may include aluminum oxide, and aluminum titanate. The feed tubeand hot chamber linings, and hot chamber pump materials may be made ofvarious ceramic materials including fused silica, aluminum oxide,aluminum titanate, zirconium oxide, and magnesium oxide; specificexamples are Al₂O₃+MgO and Al₂O₃+SiO₂ ceramics.

The overall system concept is shown below:

For illustrative purposes, the shot chamber is shown as being orientedat a 45 degree angle so as to reduce negative effects such aswaterfalling or bubbles.

Concept D: Vacuum+Inert Gas—Conventional Plunger/Shot Sleeve

System Description: A Low Pressure Pump in the Hot Chamber Feeds aMetered Shot to a “Cold” Shot Chamber (or Cold Shot Sleeve), whichForces the Melt into the Mold at Hither Pressure. Inert Gas Pressure onBack Side of Plunger Prevents Air Intrusion while Dies are Open.

-   -   The supply source of molten alloy is a hot chamber.    -   The hot chamber is maintained at a relatively constant        temperature, about 200° C. above the liquidus temperature of the        melt, through the use of insulation and heating.    -   The hot chamber feeds a cold shot chamber, comprising a plunger        housed in a “cold” shot sleeve, which drives the molten alloy        into the mold cavity. The shot sleeve is maintained at a        relatively constant temperature, below the solidus temperature        of the melt, through insulating and/or heating and/or cooling.    -   At all points in the system, and throughout the injection        process, the melt is protected from any exposure to air by a        “blanket” of an inert gas, such as argon, or by vacuum. As such,        there is a port in the shot sleeve that supplies inert gas to        the chamber on the backside of the plunger. This is key for this        system, because the plunger is not capable of positively sealing        against atmospheric pressure. The gas pressure is slightly        higher than atmospheric pressure; for example, 15 to 16 psia.        The intent is that when the dies are open, the positive gas        pressure will prevent atmosphere from leaking past the plunger        tip and into the hot chamber (as it would if the plunger        backside chamber and/or hot chamber were under vacuum).    -   This positive pressure inert gas system obviates the need for        the plunger to fully seal, thus allowing use of traditional OD        gap sealing. (That is, the small gap, or diametral clearance,        between the plunger OD and the shot sleeve ID allows so little        leakage that it provides enough of a seal to draw a reasonable        vacuum level in the mold cavity).    -   The hot chamber likewise is filled with inert gas at a similar        pressure.    -   While the dies are open, the shot chamber plunger is in the        position identified herein as Position 1 (see figures on last        page of this document). Due to the slight pressure differential        between the plunger backside chamber and atmosphere, no air will        enter the feed tube; only a slight amount of inert gas will leak        past the plunger and into the atmosphere.    -   With the shot chamber plunger still in Position 1, the dies are        closed, and vacuum is applied to the mold cavity to evacuate        oxygen that would react with the melt. A small amount of inert        gas will leak past the plunger into the mold cavity. This is        acceptable, since the objective in evacuating the mold cavity        with vacuum is not just to lower its pressure, but primarily to        remove oxygen/nitrogen that may contaminate the melt.    -   Prior to injection, the atmosphere in the mold cavity may remain        as vacuum, or it may be filled with inert gas.    -   Once a sufficient vacuum/gas quality has been achieved in the        mold cavity, the shot chamber plunger will be retracted to the        fill position, identified herein as Position 2. In this position        the shot chamber fill port communicates with the feed tube and        hot chamber, and the pump in the hot chamber fills the shot        chamber.    -   This system will work best with a positive displacement pump in        the hot chamber that can meter the shot volume (that is, deliver        a specific, predetermined amount). An ideal pump is a        piston/plunger pump similar to that of a conventional gooseneck        hot chamber system; the volume that it pumps may be controlled        by the length of its stroke. Unlike conventional hot chamber        plunger pumps, though, the components are made of a ceramic        material that can survive long term exposure to the melt without        breaking down and failing, or contaminating the melt.    -   Hot chamber pumps have an inherent pressure limitation due to        the fact that they are submerged in molten metal. The high        temperature in such an environment reduces the tensile and yield        strength of tool steels to a fraction of their strength at room        temperature. Ceramic materials also suffer a strength reduction,        though not as great, but have a further limitation in that they        have limited strength in tension. Piston cylinders are subjected        to hoop stress, which is a form of tensile stress. Further,        amorphous alloys have even higher liquidus and solidus        temperatures than those of many alloys, such as aluminum, that        are considered to be beyond the range of normal plunger pumps.        For this reason, a dual pump system is used; a low-pressure pump        in the hot chamber, which then feeds a “cold chamber” shot        sleeve adjacent to the dies. The hot chamber pump may be limited        to 1,000 psi, or even less, but the cold chamber is capable of        boosting the final pressure to 10,000 psi or greater because        temperature excursions remain below the temperature that        significantly reduce the strength of the tool steel of which it        is made.    -   Once the required shot volume is delivered from the hot chamber        to the shot chamber, the hot chamber pump shuts off and holds        fluid level in the fill tube, and the shot chamber plunger        begins to move.    -   Shot chamber plunger position is monitored by a displacement        sensor. As the shot chamber plunger reaches the position        identified as Position 3, the fill port is closed off by the        plunger; at this point the control system will command the hot        chamber pump to begin to retract. Once past Position 3, the        plunger pushes the melt into the mold cavity until pressure in        the mold cavity builds. In this system, squeeze pins are        optional but not necessary. The plunger, since it does not        bottom out on a face seal as in concepts A-C, may stroke as far        as necessary (shown below as Position 5) to apply the maximum        desired pressure to the melt.    -   On its way to full stroke, the plunger passes through Position        4, at which point the inert gas chamber on the backside of the        plunger connects to the feed tube. The retraction of the hot        chamber pump that initiated when the plunger passed Position 3        will cause a suction pressure in the melt in the feed tube, so        that when the feed port opens up to the back side chamber the        melt will be urged to retreat into the feed tube as opposed to        intruding into the back side chamber. Inert gas will fill the        feed tube from the shot chamber backside chamber.    -   The system is designed so that the melt is only in contact with        the plunger/shot sleeve for a very short duration (i.e., on the        order of a second, or less) to prevent these elements from        heating to a temperature at which 1.) their strength is reduced        beyond an acceptable level, or 2.) “soldering” of the melt to        these elements may occur.    -   In a “bottom fill” or “side fill” design, the feed tube is        connected to either the bottom, or side—as opposed to the top—of        the shot sleeve. In these designs it is desirable that after the        shot chamber has filled, the melt in the feed tube should drain        back to a predetermined level in the feed tube so that the melt        does not remain long in contact with the shot chamber plunger.        The feed tube orientation should be vertical, or angled upwards        (orientations 4 or 5 in the orientation key below) to facilitate        this draining action. The melt should only retract to a        predetermined level, though, so that on each filling stroke a        metered volume may be pumped. The hot chamber pump may be        designed with check valves on the inlet and outlet and a shuttle        piston. The shuttle piston does not allow melt to pass through,        but allows a certain amount of fluid to retract on each stroke        (see FIG. 1). This will ensure precise metering of the next        shot.    -   The hot chamber pump and shuttle piston materials should be made        of the same material, or at least from materials with a similar        coefficient of thermal expansion (CTE), so that clearances will        not change excessively at the high operating temperatures in the        hot chamber.    -   The check valve components may be made of a high-density        material such as tungsten carbide to prevent them from floating        in the melt and not seating. Alternatively, the check valves in        the pump may be loaded with rods (not shown) extending upwards        in their passages—even extending through the cover plate and out        of the hot chamber, if necessary—to provide additional sealing        force.    -   In the case of a “top fill” design it is not necessary for the        hot chamber pump to utilize the shuttle piston feature. In these        designs the feed tube is connected to the top side of the shot        sleeve (See FIGS. 2 and 3). This connection location makes it        possible for the feed tube axis to be angled with respect to a        horizontal plane (as shown in these figures), or the axis may        even be vertical (i.e., orientations 1 or 2 in the orientation        key below). The section connecting to the shot sleeve feed port        is referred to as Section 1. This section is made of a ceramic        material with low thermal conductivity (see “insulating spacer”        later in this document) to prevent heat from the feed tube,        which is heated to above the melt liquidus temperature, from        overheating the shot sleeve. The feed tube then has an elbow        that makes a turn and points downwards enters the hot chamber.        The section pointing downward to the hot chamber is referred to        as Section 2. At the top of the turn, an inert gas supply line        connects via a valve (not shown) to the feed tube.    -   While pulling vacuum in the mold cavity, the valve is open so        that any vacuum that is able to pull through the plunger OD gap        will simply pull a small amount of inert gas into the mold        cavity. Once an acceptable atmosphere in the mold cavity has        been established, the inert gas valve is closed and the plunger        is withdrawn to open the fill port to the feed tube. The hot        chamber pump is activated, pumping melt into the shot chamber.        When the hot chamber pump reaches the end of its stroke, any        melt in melt in Section 1 will drain into the shot chamber feed        port and very quickly will be injected into the mold cavity; any        melt in Section 2 will settle level with the bottom of the        inside radius of the elbow. The inert gas valve will be opened,        and melt in the feed tube elbow will be blanketed with inert gas        to prevent exposure to air.    -   In a top-fill configuration, it is useful for the melt to exit        from the feed tube into the shot chamber port through a        “nozzle”, or opening that is smaller than the size of the port,        so that the melt does not contact, wet, and adhere to the shot        sleeve around the fill port area.    -   Once the mold cavity is full and the melt in the biscuit area        that is in contact with the plunger solidifies, if desired the        plunger may be retracted to Position 1. (It may be useful to        withdraw the plunger from contact with the biscuit in order to        manage plunger temperature.) In this position, the dies may be        opened to eject the casting. The exact location of Position 1 is        not important as long as the plunger remains displaced far        enough towards the dies that the fill port is not open to        atmosphere. The fact that the shot sleeve back side chamber has        a slight positive pressure ensures that inert gas will, at most,        leak slightly past the plunger OD and prevent atmosphere from        intruding past the plunger and into the fill tube/hot chamber.    -   Since the fill port is filled by a pump, as opposed to gravity        poured, the plunger axis may be other than horizontal; even        vertical if desired. Also, the fill port may be somewhere other        than on the “high side”. In fact, it is advantageous for the        plunger to be vertical (pointed up), or closer to vertical than        to horizontal, and if angled, for the fill port to be on the low        side, or closer to the low side than to the high side (i.e.,        orientations 4 or 5, referring to the Orientation Key below).        FIG. 4, below, shows an angled plunger orientation with a        “bottom fill” feed tube/fill port orientation. In bottom-fill        configurations, the molten fluid may fill the shot chamber        smoothly without turbulence and/or “waterfalling”, a condition        which can lead to inclusion of gas/void pockets and/or premature        solidification of particulates. Turbulence and/or waterfalling        are particularly of concern if the shot chamber is (as is the        design intent) at a lower temperature than the solidus        temperature of the alloy, because the alloy may locally solidify        around gas/void pockets, and such artifacts may remain in the        final casting product as defects.    -   In fact, one of the advantages of this system is that it is not        necessary to heat the shot chamber to as high a temperature as        is required in Concepts A-C. Though some heating of the shot        sleeve may be beneficial, it may be maintained at a temperature        below the solidus temperature as long as the melt does not dwell        long enough in the shot sleeve to develop localized        solidification zones.    -   Having stated the above, the system could be configured (say,        for manufacturing convenience) with the shot chamber axis on a        horizontal plane (orientation 3). The system still maintains the        benefits of protection of the melt (by positively pressured        inert gas) from contamination by the atmosphere. In a horizontal        shot chamber axis configuration, it is still beneficial (though        not an absolute requirement) for the fill port to be on the low        side, rather than the high side, to avoid the waterfall effect.        This configuration is shown in FIG. 5 below.    -   The shot sleeve axis may also be oriented between horizontal and        vertical, pointed down (i.e., Orientation 2, referring to the        Orientation Key below). This orientation may only be used with        vacuum in the mold cavity/shot chamber, though    -   The feed tube should be continuously heated to above the solidus        temperature of the melt to prevent premature solidification of        the melt in the tube. An insulating spacer, made of a material        with low thermal conductivity (e.g., aluminum titanate ceramic)        is used between the feed tube and the shot chamber to minimize        conductive transfer of heat between the two.    -   It is advantageous for all the elements inside the hot chamber,        the hot chamber itself, and those between the hot chamber and        the insulating spacer, to be:        -   Either made of, or lined with, ceramic to avoid wetting and            reaction to/degradation from the melt        -   Heated to a constant “warm” (above solidus) temperature to:            -   Minimize thermal cycling that could break down the                ceramic and thereby contaminate the melt            -   Prevent the melt from locally solidifying at the wall                boundaries when passing through these elements. This is                particularly an issue due to the injection velocities                used, which will be much lower than those used in                conventional high pressure die casting.    -   The best ceramic valve material is considered to be fused        silica. Other options may include aluminum oxide and aluminum        titanate. The feed tube and hot chamber linings, and hot chamber        pump materials may be made of various ceramic materials        including fused silica, aluminum oxide, aluminum titanate,        zirconium oxide, and magnesium oxide; specific examples are        Al₂O₃+MgO and Al₂O₃+SiO₂ ceramics.    -   Depending on variables such as the shot volume (as defined by        casting size), casting cross-section minimum thickness, and the        extent of die heating used, the plunger and shot chamber, due to        the relatively short-term exposure (as compared to Concepts A-C)        to molten liquid, may be made of high-temperature tools steels        without compromising the ability to deliver the melt to the mold        cavity at sufficiently high enough temperature and low enough        velocity to avoid compromising casting quality. However, some        large and/or complex castings may require the plunger and/or        shot chamber also to be constructed from ceramics, and        maintained at higher temperatures (i.e., near or even above        solidus temperature).    -   Once the melt reaches the shot chamber, it is driven into the        mold cavity by a controlled plunger speed to prevent turbulence        which could cause imperfections in the finished casting. A        maximum melt velocity of 0.5 meters/sec is recommended.

The injection cycle is as follows:

Die Plunger position Position Action Feed tube Pump Open 1 (intermediateEjecting previous Connected to Off (holding position) cast part shotchamber position with back side inert melt retracted gas supply in feedtube) Closed 1 (intermediate Drawing vacuum Partially or fully Off(holding position) on mold cavity connected to shot position with(and/or filling chamber back melt retracted mold cavity with side inertgas in feed tube) inert gas) supply Closed 2 (fully Filling shot Open toshot Moving through retracted) chamber sleeve cavity full meteringstroke Closed 3 (mid stroke) Moves to position Shut off Starting atwhich plunger retraction shuts off feed port Closed 4 (mid stroke)Retraction of melt Opens to shot Retracting melt in feed tube chamberback in feed tube; side inert gas reloading supply plunger chamberClosed 5 (full stroke) Die cavity full; Connected to Off (holdingincreasing shot chamber position with pressure back side inert meltretracted gas supply in feed tube) Closed 5 (full stroke) Allowing meltin Connected to Off (holding contact with shot chamber position withplunger to solidify back side inert melt retracted gas supply in feedtube) Open 1 (intermediate Allowing casting Connected to Off (holdingposition) to cool sufficiently shot chamber position with to be ejected;back side inert melt retracted ejecting cast part gas supply in feedtube)

The above described embodiment provides a way of keeping atmosphere fromgetting in and contaminating the melt in cases where we don't want achamber that has to be heated above the solidest temperature.

The melt is going to be about a thousand degrees C./about 1800 degreesF. and about 1500 where iron-based materials get red hot. At suchtemperatures the materials lose almost if not all of their strengthproperties. (At about 1200 degrees F. is where most materials start todegrade in strength.) Thus, when trying to use a ferrous alloy at thosetemperatures, it would have no strength whatsoever and wouldn't be ableto obtain high pressure out of it. Further, it would scour and scratcheasily and there would be braising of the alloy to the steel.

Thus, this embodiment aims to keep the shot sleeve below thattemperature range, dump the molten alloy into it very quickly, andinject it very quickly.

The various combinations of atmosphere and feed methods are shown in thetable below:

Discussion

The unique advantages of this system are:

-   -   Provides a means of sealing the melt system from exposure to the        atmosphere while the dies are open, but due to the positive        pressure in the hot chamber and plunger back side chamber, does        not rely as heavily as Concepts A-C on the extent to which the        cold chamber plunger can positively seal in order to hold        vacuum.    -   Provides a means (i.e., a low pressure pump in the hot chamber)        of metering an exact shot volume to the mold cavity along with        the means (i.e., a cold chamber shot sleeve) to generate high        pressure at the end of the injection cycle.    -   Provides a means (i.e., the shuttle piston) of retracting the        melt from contact with the cold shot sleeve to prevent it from        overheating.    -   The shot chamber may utilize a bottom-fill feed port, and also        may be oriented in orientations 4 or 5, both of which offer a        less-turbulent flow profile than other orientations.    -   The system has a minimum of complexity; in particular, there are        no valves that must seal against both melt and vacuum.

The shot chamber or shot sleeve doesn't necessarily have to bemaintained above the solidest temperature of the alloy.

Typically when the dies are open, air can leak past the plunger into themelt chamber and it will contaminate the melt. Once the dies are closedit can also take a long time to draw a vacuum and suck the air back outof that chamber. This disclosure solves the challenge of making theprocess more efficient by simply pressurizing that chamber that housesthe crucible/ladle with inert gas at slightly higher than atmosphericpressure (e.g., 15-16 psi atmospheric).

In accordance with an embodiment, the shot chamber is oriented somewherebetween vertical and horizontal (e.g., pointing upwards toward the die,as opposed to being horizontal as a conventional shot chamber normallyis).

The hot chamber pump with the shuttle piston is shown below in FIG. 1:

FIG. 2, below, shows the feed tube and nozzle configuration used inconjunction with a top-feed, horizontally-oriented shot sleeve (shown inthe mode of pulling vacuum):

FIG. 3, below, shows the feed tube and nozzle configuration used inconjunction with a top-feed, horizontally-oriented shot sleeve (shownhere in the mode of filling the shot sleeve with melt):

The overall system concept in Configuration D1, with the plunger inorientation 4 (angled, pointed up) is shown below in FIG. 4:

The overall system concept in Configuration D1, with the plunger inorientation 3 (horizontal) is shown below in FIG. 5:

The terminology for Concept D is shown below (note that the shot sleeve,insulating spacer, and bushing are sectioned for clarity):

The images below are typical of both concept D1 and D2; the onlydifference in D2 is that the mold cavity is first evacuated with vacuum,then filled with inert gas.

In this position (position 1, above), the dies are open and basicallywe're just holding the plunger where it's stroked out, at its laststroke, or retracted a little bit, so it doesn't maintain contact withthe biscuit as it's solidifying or as it's still real hot. In thisposition, this plunger backside area connects to the port that suppliesit with inert gas and the inert gas also goes down and fills the feedtube. So everything is surrounded by inert gas that's at a slightlyhigher pressure than atmospheric pressure.

Position four shows where the piston first begins to open up the feedtube to that backside chamber and now inert gas can push the melt, orreally just allow the melt to fall back down the feed tube and back intothe hot chamber.

Concept E: Two Valves Inline Forming a Metering Chamber Between HotChamber and Cold Shot Chamber

System Description: A Low Pressure Pump Feeds Melt from a Hot Chamber toa Metering Chamber, which Feeds a Cold Shot Chamber. The MeteringChamber Volume is Defined by the Space Between Two Valves. The ValvesAlso Isolate the Melt in the Feed Tube/Hot Chamber from Exposure to Airwhile the Dies are Open. Final High Pressure Injection is Provided bythe Cold Shot Chamber.

-   -   The supply source of the melt is a hot chamber.    -   The hot chamber is maintained at a relatively constant        temperature, about 200° C. above the liquidus temperature of the        melt, through the use of insulation and heating.    -   The hot chamber feeds a metering chamber, created by two valves        positioned inline between the hot chamber and the shot sleeve.        The volume of the passage between the two valves serves to        define the volume of each shot. The metering chamber is        designed, by its inside diameter (or other cross-section        dimensions) and length, to meter the shot.    -   The lowermost of the two valves serves to isolate the melt from        atmosphere while the dies are open.    -   The method of feeding melt from the hot chamber to the metering        chamber/cold chamber may be a pump, a pressure differential        created by inert gas, or gravity.    -   The metering chamber feeds a cold shot chamber, comprising a        plunger housed in a “cold” shot sleeve, which drives the molten        alloy into the mold cavity. The shot sleeve is maintained at a        relatively constant temperature, below the solidus temperature        of the melt, through insulating and/or heating and/or cooling.    -   At all points in the system, and throughout the injection        process, the melt is protected from any exposure to air by a        “blanket” of an inert gas, such as argon, or by vacuum.    -   Prior to injection, the mold cavity is purged by vacuum to        evacuate oxygen that would react with the melt.    -   On the first cycle, the lower valve must be left open during        vacuum purging; the metering chamber must be evacuated in order        to be filled completely by melt. During evacuation, the plunger        should be withdrawn to the “fill” position, opening the shot        chamber fill port to the fill tube, to allow any air to evacuate        quickly from the fill tube and metering chamber body. On        subsequent cycles, the metering chamber will remain in a vacuum        state as long as the lower valve is left closed while the dies        are open, so repeated evacuation of the metering chamber is not        necessary.    -   Both valves must withstand continuous exposure to molten alloy,        and must be maintained (as a minimum) above the solidus        temperature of the alloy.    -   Since the upper valve isolates the melt from exposure to air        while the dies are open, the plunger/shot sleeve does not have        to perform this function. The plunger thus may utilize        conventional diametral gap clearances, and the plunger itself        does not have to effect a positive seal to the shot sleeve. The        plunger and shot sleeve thus need not be heated beyond the usual        requirements for conventional die casting.    -   The feed tube from the hot chamber to the valves, both valves,        and the metering chamber must all be maintained (by use of        heating elements and/or insulation) at a temperature above the        solidus temperature of the melt, to prevent the melt from        solidifying between a valve and mating seat and “brazing” the        two together.    -   Although the melt may be transferred from the hot chamber to the        metering chamber by various methods, the melt is transferred        from the metering chamber to the shot chamber by gravity. Thus,        the metering chamber body (i.e., tube) and the inlet tube        connecting the lower valve and the shot sleeve fill port        optimally should be inclined at an angle that is sufficiently        high enough (with respect to horizontal) that the melt will flow        quickly, but low enough that the melt flows smoothly without        turbulence. 10 degrees to 45 degrees is considered to be an        optimum range.    -   As such, the shot chamber fill port must be on the top, or near        the top side of the shot sleeve (not on the bottom).    -   Due to the necessary orientation of the fill tube, this concept        may only be used with vacuum (not gas) in the mold cavity. If        gas were used, as the melt were to fill the shot chamber, the        gas would rise upwards and be trapped in the metering chamber        near the top valve. (This would prevent accurate metering of        subsequent shots.)    -   The orientation (see Orientation Key, below) of the shot        sleeve/plunger axis may be horizontal, or inclined between        vertical and horizontal (i.e., orientations 3 or 2,        respectively). Each may have advantages and disadvantages, but a        horizontal (orientation 3), or near-horizontal, shot sleeve        orientation is preferable because the shot chamber can be filled        completely before starting injection into the mold cavity. (In        orientations 1 or 2, the melt will begin to fill the mold cavity        before the shot chamber is full, and there is a risk of the melt        beginning to solidify prematurely.)    -   As with Concept D, it is beneficial to use a nozzle at the fill        port so that the melt does not contact, and wet, the feed port        itself (see FIG. 2, at end of document).    -   One of the advantages of this system is that it is not necessary        to heat the shot chamber to as high a temperature as is required        in Concepts 1-4. Though some heating of the shot sleeve may be        beneficial, the design intent of this system is to maintain the        shot sleeve below the solidus temperature of the melt. To do so,        injection rates must be fast enough that the melt is not allowed        to dwell long enough in the shot sleeve to develop localized        solidification zones.    -   It is necessary for all the elements lining, and inside, the hot        chamber, and those between the hot chamber and lower valve        (including valves and valve bodies), to be:        -   Made of ceramic to avoid wetting and reaction to/degradation            from the melt        -   Heated to a constant temperature (above the solidus            temperature of the melt) to:            -   Minimize thermal cycling that could break down the                ceramic and thereby contaminate the melt            -   Prevent the melt from locally solidifying at the wall                boundaries when passing through these elements. This is                particularly an issue due to the injection velocities                used, which will be much lower than those used in                conventional high pressure die casting.    -   The best ceramic valve and valve seat material is considered to        be fused silica. Other options may include aluminum oxide, and        aluminum titanate. The feed tube and hot chamber linings, and        hot chamber pump materials may be made of various ceramic        materials including fused silica, aluminum oxide, aluminum        titanate, zirconium oxide, and magnesium oxide; specific        examples are Al₂O₃+MgO and Al₂O₃+SiO₂ ceramics.    -   As the valves are heated above the solidus temperature of the        melt, but the shot sleeve is designed to remain below that        temperature, the inlet tube between the lower valve and the shot        sleeve is a ceramic material selected for low thermal        conductivity and high resistance to thermal shock. An exemplary        material is aluminum titanate.    -   Depending on variables such as the shot volume (as dictated by        casting size), casting cross-section minimum thickness, and the        extent of die heating used, the plunger and shot chamber, due to        the relatively short-term exposure (as compared to Concepts 1-4)        to molten liquid, may be made of high-temperature tools steels        without compromising the ability to deliver the melt to the mold        cavity at sufficiently high enough temperature and low enough        velocity to avoid compromising casting quality. However, some        large and/or complex castings may require the plunger and/or        shot chamber also to be constructed from ceramics, and        maintained at higher temperatures (i.e., near or above solidus        temperature).    -   Although the plunger tip is not required to seal against vacuum        in this design, the plunger rod must still hold a vacuum seal        (or, the shot sleeve and the plunger actuator must either be        enclosed in a vacuum chamber) so that vacuum can effectively be        established once the dies are closed. It is beneficial to        provide a separate vacuum port to the plunger backside chamber,        so that the vacuum applied to this area does not have to travel        through the die cavity and around the plunger OD gap.    -   Once the dies close, the vacuum source(s) for the mold cavity        may also serve to evacuate the shot chamber cavity.    -   Once the melt reaches the shot chamber, it is driven into the        mold cavity by a controlled plunger speed to eliminate        turbulence which could cause imperfections in the finished        casting. A maximum melt velocity of 0.5 meters/sec is        recommended.

The injection cycle is as follows:

Die Plunger Lower Upper position Position Action valve valve Pump Closed2 (fully Drawing vacuum Closed Open On retracted) on mold cavity;filling metering chamber Closed 2 (fully Filling shot Open Closed Offretracted) chamber Closed Moving from Injecting melt Closed Open On 2 to3 into mold cavity Closed 3 (full Allowing casting Closed Open Onstroke) to solidify Open 1 (intermediate Ejecting cast Closed Open Onposition) part; filling metering chamber

Note that the pump may be “on” as long as the lower valve is closed(which allows the upper valve to be open). However, it may not benecessary to run the pump for such a large percentage of the overallcycle.

The various combinations of atmosphere and feed methods are shown in thetable below:

Discussion

The advantages of this system are:

-   -   Provides a positive means of isolating the melt system from        exposure to the atmosphere while the dies are open, but without        requiring the plunger to seal, thus allowing use of a        conventional cold chamber shot sleeve system.    -   The two-valve-based metering system eliminates the need for a        metering pump in the hot chamber. In fact, this system provides        a means of metering an exact shot volume to the die without        using a metering pump or flow sensors, even if using gravity or        gas pressure as the feed method.    -   Provides an effective system for using only vacuum (not inert        gas) to establish an inert atmosphere in the mold cavity and        shot sleeve.

The overall system concept (version with horizontal shot sleeve) isshown in FIG. 1, below:

This embodiment provides the ability of getting a metered shot byputting two valves in the system prior to the shot chamber. The valvesare between the hot chamber and the shot chamber. In this concept, theplunger doesn't have any means of the sealing against atmosphere. Thelower most of those two valves will be closed when the dies are open.When the dies are open, atmosphere can enter into the plunger cavity.Once the dies are closed, a vacuum is pulled on the mold cavity thatwill also suck the air out of the plunger cavity (i.e. the shotchamber). In the meantime, the top valve is opened and the feed tubebetween the two valves fills up with a specific volume. That volume isdefined by the length and the diameter of that feed tube. Once vacuumhas been established, with the die closed, the bottom valve is openedand the melt is allowed through and then shot it into the dies.

In accordance with an embodiment, this disclosed concept uses gravityfeed. In another embodiment, the same two valve configuration is usedwith a pump.

A nozzle may be used to prevent wetting of feed port in top-fillconfiguration:

An example valve is shown below:

As for the materials and type of valve, in one embodiment, both the bodyof the valve and the valve stopper itself are made from ceramic. Inanother embodiment, at least the valve stopper is made of ceramic. Inyet another embodiment, the valve stopper and stem are made of ceramic.The valve needs to be heated above the solidest temperaturecontinuously. In an embodiment, the valve may be manufactured such thatthe area of the seat of this valve and its angle is such that thereisn't a surface that's horizontal, so that the melt never touches asurface that's horizontal. The valve has to be kept heated so that thematerial never braises, it never solidifies and braises the valve to thebody.

To get rid of any air in or around the valves, when the dies are open,the plunger is left in its fully extended position so that there's onlya small gap between the plunger and the inside diameter of the shotchamber. Any air that leaks in will be done slowly so it doesn't createthermal shock for that valve. Then there is drawing vacuum on the diesonce the dies are closed. Once vacuum on the dies is being drawn, theplunger is pulled back so that it's open to the feed port and thereforeopen to this passage below the bottom of the valve and suck all the airout of there.

Concept F: One Valve Inline Between Hot Chamber and Cold Shot Chamber

System Description: Combination hot chamber/cold shot chamber system.Final injection is provided by a cold shot chamber. A valve in the feedtube, proximal to the shot chamber, isolates the melt from atmospherewhile the dies are open. The shot must be metered by the hot chamberpump and/or control system.

(Note: This system is similar in many respects to Concepts D and E. Theuse of a valve is similar to that of Concept E, but since there is onlyone valve, shot metering must be performed by a means other than ametering chamber. As with Concept D, the metering function is providedby either by a positive displacement hot chamber pump, or by anon-positive displacement pump combined with flow sensor(s) and acontrol system.

-   -   The supply source of the melt is a hot chamber.    -   The hot chamber is maintained at a relatively constant        temperature, about 200° C. above the liquidus temperature of the        melt, through the use of insulation and heating.    -   The hot chamber feeds a “cold” chamber that drives the molten        alloy into the mold cavity. The cold chamber comprises a shot        chamber plunger housed in a shot sleeve. The shot sleeve is        maintained at a relatively constant temperature (below the        solidus temperature of the melt) through insulating and/or        heating and/or cooling.    -   At all points in the system, and throughout the injection        process, the melt is protected from any exposure to air by a        “blanket” of an inert gas, such as argon, or by vacuum.    -   Prior to injection, the mold cavity is purged by vacuum to        evacuate oxygen that would react with the melt.    -   After purging, the mold cavity may be left in the vacuum state        for injection, or may be filled with inert gas.    -   In addition, in this concept, a valve is positioned inline in        the feed tube between the hot chamber and the shot sleeve. The        function of the valve is to isolate the melt from atmosphere        while the dies are open.    -   The valve must withstand continuous exposure to molten alloy,        and must be maintained (as a minimum) above the solidus        temperature of the alloy.    -   Unlike Concept E, there is no separate metering chamber between        the hot chamber pump and the shot chamber. Rather, as with        Concept D, the metering function must be performed by the hot        chamber pump. As with Concept D, a positive displacement pump is        the best method of feeding melt from the hot chamber to the cold        chamber.    -   A piston pump such as described in Concept D may be used. As in        Concept D, it is desirable for the melt to retract down the feed        tube to minimize contact between the melt and the plunger/shot        sleeve, to keep those elements from overheating. The        functionality and material requirements are the same as        described in Concept D.    -   Alternatively, gas pressure in the hot chamber (at a higher        pressure than that of gas, if used, in the mold cavity) or        gravity feed could be used to transfer the melt from the hot        chamber to the cold shot chamber. Flow sensors would be required        to allow the pump to be shut off at the correct time.    -   The inline feed tube valve must be left open during the plunger        stroke to allow the melt to retract. The valve may only be        closed once the melt has retracted to a level below that of the        valve.    -   As with Concept E, the feed tube from the hot chamber and the        inline valve must each be maintained (by use of heating elements        and/or insulation) at a temperature above the solidus        temperature of the melt, to prevent the melt from solidifying        between a valve and mating seat and “brazing” the two together.    -   As with Concepts D and E, an inlet tube or insulating spacer        tube connects the inline valve and the shot sleeve. This element        should be made of a ceramic material with low thermal        conductivity and high thermal shock resistance. An exemplary        material is aluminum titanate.    -   As with Concept E, since the inline feed tube valve isolates the        melt, the plunger/shot sleeve does not have to perform this        function. It may thus utilize conventional diametral gap        clearances, and the plunger itself does not have to effect a        positive seal to the shot sleeve. The plunger and shot sleeve        also need not be heated beyond the usual requirements for        conventional die casting.    -   Since the valve positively isolates the melt, though, the range        of inert atmosphere options is wider than those of Concept D; in        fact, the same as Concept E. Specifically, vacuum may be used as        an alternative to inert gas in the plunger backside chamber, and        also may be used in the hot chamber.    -   Unlike Concept E, gravity is not required in the final transfer        of melt into the cold shot chamber. As such, the same range of        shot chamber and feed tube orientations may be used as in        Concept D.    -   As with Concepts D and E, with the shot chamber in, or near, the        horizontal orientation (orientation 3) it is beneficial to use a        nozzle at the fill port so that the melt does not contact, and        wet, the feed port itself (see FIG. 2, at end of document).    -   As with Concepts D and E, the shot sleeve should only be        positioned in orientations 1 and 2 only when used with vacuum in        the shot chamber/mold cavity. (If used with gas, the melt would        settle to the lower region of the shot chamber, and gas would be        trapped near the plunger. Once the plunger were to drive the        melt into the mold cavity, some gas may remain near the        plunger/biscuit area, and some may migrate as bubbles that may        become trapped in the solidified casting . . . an undesirable        effect.)    -   One of the advantages of this system is that it is not necessary        to heat the shot chamber to as high a temperature as is required        in Concepts 1-4. Though some heating of the shot sleeve may be        beneficial, the design intent of this system is to maintain the        shot sleeve below the solidus temperature of the melt. To do so,        injection rates much be fast enough that the melt may not be        allowed to dwell long enough in the shot sleeve to develop        localized solidification zones.    -   It is necessary for all the elements lining, and inside, the hot        chamber, and those between the hot chamber and lower valve        (including valves and valve bodies), to be:        -   Either made of, or lined with, ceramic to avoid wetting and            reaction to/degradation from the melt        -   Heated to a constant temperature (above the solidus            temperature of the melt) to:            -   Minimize thermal cycling that could break down the                ceramic and thereby contaminate the melt            -   Prevent the melt from locally solidifying at the wall                boundaries when passing through these elements. This is                particularly an issue due to the injection velocities                used, which will be much lower than those used in                conventional high pressure die casting.    -   The best ceramic valve and valve seat material is considered to        be fused silica. Other options may include aluminum oxide, and        aluminum titanate. The feed tube and hot chamber linings, and        hot chamber pump materials may be made of various ceramic        materials including fused silica, aluminum oxide, aluminum        titanate, zirconium oxide, and magnesium oxide; specific        examples are Al₂O₃+MgO and Al₂O₃+SiO₂ ceramics.    -   As the valves are heated above the solidus temperature of the        melt, but the shot sleeve is designed to remain below that        temperature, the inlet tube between the lower valve and the shot        sleeve is a ceramic material selected for low thermal        conductivity and high resistance to thermal shock. An exemplary        material is aluminum titanate.    -   Depending on variables such as the shot volume (as dictated by        casting size), casting cross-section minimum thickness, and the        extent of die heating used, the plunger and shot chamber, due to        the relatively short-term exposure (as compared to Concepts 1-4)        to molten liquid, may be made of high-temperature tools steels        without compromising the ability to deliver the melt to the mold        cavity at sufficiently high enough temperature and low enough        velocity to avoid compromising casting quality. However, some        large and/or complex castings may require the plunger and/or        shot chamber also to be constructed from ceramics, and        maintained at higher temperatures (i.e., near or above solidus        temperature).    -   As with Concept E, although the plunger tip is not required to        seal against vacuum in this design, the plunger rod must still        hold a vacuum seal (or, the shot sleeve and the plunger actuator        must either be enclosed in a vacuum chamber, or in a chamber        filled with inert gas) so that vacuum can effectively be        established once the dies are closed.    -   Once the dies close, the vacuum source(s) for the mold cavity        may also serve to evacuate the shot chamber cavity.    -   Once the melt reaches the shot chamber, it is driven into the        mold cavity by a controlled plunger speed to eliminate        turbulence which could cause imperfections in the finished        casting. A maximum melt velocity of 0.5 meters/sec is        recommended.

The injection cycle is as follows:

Die Plunger Lower position Position Action valve Pump Open 1(intermediate Ejecting previous Closed Off position) cast part Closed 2(fully Drawing vacuum on Closed retracted) mold cavity; filling meteringchamber Closed 2 (fully Drawing vacuum on Closed retracted) mold cavityClosed 2 (fully Filling shot chamber Open retracted) Closed 2 (fullyShot chamber full Closed retracted) Closed 2-3 Injecting melt intoClosed mold cavity Open 3 (full Allowing casting Closed stroke) tosolidify Open 1 (intermediate Ejecting cast part Closed position)

The various combinations of atmosphere and feed method are shown in thetable below:

Discussion

The unique advantages of this system are:

-   -   Provides a positive means of isolating the melt system from        exposure to the atmosphere while the dies are open, but without        requiring the plunger to seal, thus allowing use of a        conventional cold chamber shot sleeve system.    -   Provides a means of metering an exact shot volume to the die.    -   Allows a wider variety of shot chamber and feed tube        orientations than Concept E. In particular, the shot chamber may        utilize a bottom-fill feed port, and also may be oriented in        orientations 4 or 5, both of which offer a less-turbulent flow        profile than other orientations.    -   Provides an effective system for using only vacuum (not inert        gas) to establish an inert atmosphere in the mold cavity and        shot sleeve.

What is claimed is:
 1. A method comprising: providing an amorphous alloyto a melting chamber in an injection system, the injection system alsocomprising a mold cavity for molding the alloy, and the melting chamberand the mold cavity being maintained in an inert atmosphere; heating themelting chamber to or above a solidus temperature of the amorphous alloyto form a hot chamber; melting the amorphous alloy within the hotchamber to form molten alloy; supplying the molten alloy from the hotchamber to the mold cavity using a valve system; and molding the moltenalloy into a molded part using the mold cavity, wherein the valve systemis configured to inject a metered amount of the molten alloy into themold cavity.
 2. The method of claim 1, wherein the injection systemfurther comprises a feed tube extending from the hot chamber to thevalve system, and wherein the method further comprises supplying themolten alloy from the hot chamber to the feed tube, and supplying themetered amount of the molten alloy from the feed tube into the moldcavity.
 3. The method of claim 1, wherein the valve system comprises aplunger housed in a shot sleeve, and wherein the method furthercomprises supplying molten alloy from the hot chamber to the shotsleeve, and injecting the metered amount of the molten alloy into themold cavity using the plunger.
 4. The method of claim 3, furthercomprising using the plunger to meter a volume of molten alloy beforethe injecting into the mold cavity.
 5. The method of claim 3, furthercomprising heating the plunger and the shot sleeve to or above thesolidus temperature of the amorphous alloy.
 6. The method of claim 3,wherein the plunger comprises a plunger tip, and wherein the methodfurther comprises sealing the molten alloy within the shot sleeve fromatmospheric air using the plunger tip.
 7. The method of claim 1, furthercomprising using gravity or pressure from a pump as part of the valvesystem to meter a volume of molten alloy for injection into the moldcavity.
 8. The method of claim 1, wherein the inert atmosphere isprovided via a vacuum using a vacuum source or an inert gas using aninert gas source.
 9. An injection system comprising: a melting chamberand a mold cavity, the melting chamber being configured to receive anamorphous alloy for melting into molten alloy and configured be heatedby a heat source to or above a solidus temperature of the amorphousalloy to form a hot chamber for containing the molten alloy and the moldcavity being configured to mold the molten alloy into a molded part,both the melting chamber and the mold cavity being configured to bemaintained in an inert atmosphere; and a valve system between the hotchamber and the mold cavity for supplying the molten alloy from the hotchamber to the mold cavity, wherein the valve system is configured toinject a metered amount of the molten alloy into the mold cavity. 10.The system of claim 9, wherein the injection system further comprises afeed tube extending from the hot chamber to the valve system, andwherein the feed tube is configured to receive the molten alloy from thehot chamber and supply the metered amount of the molten alloy into themold cavity.
 11. The system of claim 9, wherein the valve systemcomprises a plunger housed in a shot sleeve, and wherein the shot sleeveis configured to receive molten alloy from the hot chamber and theplunger is configured to inject the metered amount of the molten alloyinto the mold cavity.
 12. The system of claim 11, wherein the shotsleeve is oriented at an acute angle relative to a horizontal axis. 13.The system of claim 11, the plunger is oriented at an acute anglerelative to a horizontal axis.
 14. The system of claim 9, wherein thevalve system is configured to use gravity or pressure from a pump tometer a volume of molten alloy for injection into the mold cavity. 15.The system of claim 9, wherein the inert atmosphere is provided via avacuum using a vacuum source or an inert gas using an inert gas source.